This research program is aimed at understanding how thrombin is generated and how thrombin generation is regulated. Our approach to these questions comes via the convergence of four separate directions associated with 1) the physical properties of coagulation enzyme complexes, their constituents and how these complexes can assemble into efficient enzyme catalysts. 2) Studies in which multiple coagulation catalysts/inhibitors are mixed to attempt to duplicate the performance of the combined catalyst system associated with the tissue factor pathway of thrombin expression. 3) To study this process in minimally modified biological systems (whole blood) to evaluate the correctness of hypothesis derived from purified systems. 4) To create mathematical models which can be used to define, on a quantitative basis, the process of blood clotting and its regulation both to aid in experimental designs 1,2,3, and also to aid in the evaluation of the pharmacologic agents and the diagnosis and treatment of hemostatic and thrombotic diseases. The aim of the present investigation is to understand the nature of procoagulant and anticoagulant vitamin-K dependent complexes and their regulation during the process of thrombin generation. Studies will employ physical chemistry techniques including hydrodynamics and fluorescence spectroscopy, (the latter both in solution and on surfaces) in closed systems and under flow to study complexes on synthetic membranes and cells. Reactions will be followed using both synthetic and natural substrates to monitor both presteady state and steady state kinetic events. Natural and recombinant inhibitors will be used to study the regulation of procoagulant and anticoagulant processes associated with thrombin generation. We will integrate the detailed information available through studies of individual reactions with that obtained from multi-reaction center systems. Conversely, the processes noted to occur in the whole blood system will direct appropriate attention in the purified system analyses. We anticipate developing a quantitative evaluation of the biologically relevant chemistry associated with the complex reactions which occur simultaneously during a blood clotting event. These data have significance in interpreting normal physiology and in developing approaches to correct the coagulation pathology associated with thrombosis and hemophilia. The techniques we develop will provide tools for the evaluation of potential pharmacological intervention in hemostatic and thrombotic disease.